Ancient, highly active galaxies discovered

Pasadena, CA — Using information gathered from several telescopes, a team of astronomers, including Carnegie’s Eric Murphy, searched the sky for very rarely seen dusty starburst galaxies, formed soon after the Big Bang. These galaxies are characterized by an unusually high rate of star formation. They are much more abundant in the early Universe than previously thought. Two of those identified are among the oldest ever found, indicating that these dusty starbursts likely evolve into the most massive galaxies ever observed in the local Universe. The results are published online March 13 by Nature.

The most intense bursts of starbirth are thought to have taken place in the early Universe in massive, bright galaxies containing lots of cosmic dust. By looking far into space, at galaxies which are so distant that their light has taken many billions of years to reach us, astronomers can observe this busy period of the Universe’s youth.

“The more distant the galaxy, the further back one is looking, so by measuring their distances we can piece together a timeline of how vigorously the Universe was making new stars at different stages of its 13.7 billion year life,” said lead author Joaquin Vieira of the California Institute of Technology.

Obtaining detailed information about massive starbursting galaxies at such early epochs has been extremely difficult owing to the fact that they contain immense densities of dust. In the local Universe (which stretches out 380 million light years), such dusty starbursts appear to be formed by the collision of two galaxies, which powers the subsequent star genesis.

The team used data gathered from the South Pole Telescope (SPT) to select a sample of 26 potentially lensed, dusty starburst galaxies and then used the Atacama Large Millimeter Array (ALMA) to obtain both imaging and spectroscopy. The imaging data demonstrated that these sources are strongly lensed by foreground galaxies, which increases their apparent luminosities by a factor of ~10, which translates to a savings in telescope time of ~100, and allows such distant and intrinsically faint objects to be more easily detected. The spectroscopic observations provided redshifts for the sources and information on their gas content (the fuel for star formation).

From these observations, the team was able to roughly double the number of known starburst galaxies that exist in the so-called high-redshift (z > 4) Universe. A galaxy’s redshift value is a measurement of how much the wavelength of the light from it that reaches Earth is stretched by the expansion of the Universe. Thus, it reveals the galaxy’s age and distance. Two of the galaxies are at a redshift of 5.7, which means they formed stars 1 billion years after the Big Bang.

“This newly discovered population of high-redshift, dusty starburst galaxies will help improve our understanding of star formation in the early Universe. It demonstrates that large reservoirs of molecular gas and dust can be present in massive galaxies at very early times.” Murphy said. “What’s more, the fact that out of just 26 potential galaxies, we found two of the oldest starbursts ever observed bodes well for future discoveries.”

The astronomers used only a partial array of 16 of ALMA’s full complement of 66 giant antennas, because the observatory was still under construction. When complete, ALMA will be even more sensitive, and will be able to detect even fainter galaxies.

Caption: Light rays from a distant galaxy are deflected due to the gravity of a massive, foreground galaxy, as predicted by Einstein's theory of general relativity. This makes the background galaxy appear as multiple magnified images surrounding the foreground galaxy. This type of gravitational lensing allowed such distant and intrinsically faint objects as the dusty starburst galaxies in this study to be more easily detected. Image is courtesy of ALMA (ESO/NRAO/NAOJ), Luis Calcada, and Yashar Yezaveh. For a larger view, click here

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The South Pole Telescope (SPT) is a 10-meter telescope located at the National Science Foundation (NSF) Amundsen-Scott South Pole Station within 1 km of the geographic South Pole. The SPT is designed to conduct low-noise, high-resolution surveys of the sky at millimeter (mm) and submillimeter (submm) wavelengths, with the particular design goal of making ultra-sensitive measurements of the cosmic microwave background (CMB). The first major survey with the SPT was completed in October, 2011 and covers 2500 square degrees of the southern sky in three mm-wave observing bands. This is the deepest large mm-wave dataset in existence and has already led to many groundbreaking science results, including the first galaxy clusters detected through their Sunyaev-Zel'dovich effect signature, the most sensitive measurement yet of the small-scale CMB power spectrum, and the discovery of a population of ultra-bright, high-redshift, star-forming galaxies. The SPT is funded primarily by the Division of Polar Programs in NSF's Geosciences Directorate. Partial support also is provided by the NSF-funded Physics Frontier Center of the KICP, the Kavli Foundation, and the Gordon and Betty Moore Foundation.The SPT collaboration is led by the University of Chicago and includes research groups at Argonne National Laboratory, California Institute of Technology, Cardiff University, Case Western Reserve University, Harvard University, Ludwig-Maximilians-Universität, Smithsonian Astrophysical Observatory, McGill University, University of Arizona, University of California at Berkeley, University of California at Davis, University of Colorado at Boulder, University of Michigan, as well as individual scientists at several other institutions, including the European Southern Observatory and the Max-Planck-Institut für Radioastronomie in Bonn, Germany.

ALMA is a partnership of ESO, NSF, NINS, NRC, NSC and ASIAA, in cooperation with the Republic of Chile. The Joint ALMA Observatory is operated by ESO, AUI/NRAO and NAOJ. The National Radio Astronomy Observatory is a facility of the NSF, operated under co-operative agreement by Associated Universities Inc. The work is based, in part, on observations made with Herschel, a European Space Agency Cornerstone Mission with significant participation by NASA and supported through and award issued by JPL/Caltech.

This work was partially supported by NASA, the Science and Technologies Facilities Council NSERC, the CRC program and CIfAR.